J. Szatkowski

Growth and characterisation of Zn1−xBexSe mixed crystals

Abstract Beryllium containing, wide-gap II–VI semiconducting compounds may offer a possibility of a significant reduction of the defect propagation in the active region and therefore increasing of II–VI lasers lifetimes due to more covalent bonding and lattice hardening [1] [Ch. Verie, in: B. Gil, R.L. Aulombard (Eds.), Semiconductor Heteroepitaxy, Growth, Characterization and Device Applications, World Scientific, Singapore, 1995, p. 73]. Until now, the published papers were concerned thin films [2,3] [F. Fischer, G. Landwehr, Th. Litz, H.J. Lugauer, U. Zehnder, Th. Gerhard, W. Ossau, A. Waag, J. Crystal Growth 175–176 (1997) 532; V. Bousquet, E. Tournie, M. Laugt, P. Vennegues, J.P. Faurie, Appl. Phys. Lett.70 (1997) 3564] but the fundamental properties of Zn 1− x Be x Se bulk crystals have not been investigated as yet. This work deals with an experimental study of structural and photoluminescence properties of Zn 1− x Be x Se mixed crystals as a function of composition.

Growth and characterisation of Cd1−xMgxSe mixed crystals

Cd 1-x Mg x Se mixed crystals for 0 < x < 0.55 have been grown by the high-pressure Bridgman method under an argon overpressure. The dependence of the energy gap, the luminescence and the electrical properties on the Mg concentration has been investigated. Luminescence and transmission spectra show that the band-gap energy is considerably larger than that of pure CdSe and for Cd 0.45 Mg 0.55 Se we measured about 2.82 eV at T = 40 K. As grown Cd 1-x Mg x Se solid solutions with x < 0.4 exhibit n-type conductivity and low electrical resistivity (ρ < 1 Ω cm at room temperature). The maximum of electron concentration 1.3 x 10 18 cm -3 was obtained for Cd 0.85 Mg 0.15 Se. An attempt to explain the dependence of free-carrier concentration on composition by a model of Fermi-level pinning is presented.

Deep hole traps in Be-doped Al0.5Ga0.5As layers grown by molecular beam epitaxy

Deep hole traps in p-type Al0.5Ga0.5As grown by molecular beam epitaxy have been studied by the deep-level transient-spectroscopy method applied to samples with a Schottky diode configuration. Five hole traps, labeled as H0 to H4, were found. For traps H1, H3, and H4 the activation energies for emission were ET1=0.14 eV, ET3=0.40 eV, and ET4=0.46 eV, respectively. Hole emission from trap H2 was dependent on the external electric field. The emission rate obeyed the Poole–Frenkel relation. When extrapolated to zero electric field, the thermal activation energy for hole emission was ET2,0=0.37 eV. Capture cross sections for traps H1 and H4 were thermally activated with energy barriers EB1=0.04 eV and EB4=0.18 eV, respectively.

Growth and characterisation of bulk Zn1−xBexSe, Zn1−x−yMgxBeySe and Zn1−xBexTe crystals

Abstract In this paper we report an extension of our earlier results for Zn 1− x Mg x Se and low-Be Zn 1− x Be x Se to related ternary (high-Be Zn 1− x Be x Se and Zn 1− x Be x Te) and quaternary (Zn 1− x − y Mg x Be y Se) alloys. A dependence of defect structure on crystal composition, growth and thermal treatment is observed. X-ray diffraction was used for phase analysis and determination of lattice parameters. High-resolution transmission electron microscopy was used to compare kind and density of defect. Among the studied crystals, the lowest defect density was found for Zn 1− x − y Mg x Be y Se.

Persistent photoconductivity and DLTS in indium-doped Cd0.9Mn0.1Te

Abstract The properties of an indium-related DX center were determined in indium-doped Cd0.9Mn0.1Te by deep-level transient spectroscopy (DLTS). These studies, carried out within a 77–360K temperature range, revealed the presence of five electron traps. It was possible to determine the activation energy for four of them. Their values were equal to 0.22–0.30, 0.43, 0.51 and 0.63 eV, respectively. For the first energy level, the concentration of the associated traps was higher than 10% of the concentration of the shallow levels and the capture cross section was thermally activated, with an energy barrier for capture equal to 0.1 eV. The concentration of the other three traps was lower than 10 14 cm −3 . Persistent photoconductivity was also observed at low temperatures. At 77 K, the photoconductivity continued for a very long time after the light was extinguished, and was present until the temperature of the sample increased to 170 K. The very high concentration and thermally activated capture cross section for the first trap suggest its DX center nature.

Persistent photoconductivity in high resistive Zn3P2

Resistivity and photoconductivity of p-type Zn3P2 polycrystals grown by closed tube vapour transport method have been investigated. Persistent photoconductivity (PPC) has been observed at temperatures T < 200 K. At 77 K, the photoconduction persists for over 103 s after termination of the light. The PPC buildup and decay kinetics have been measured at 77 K and analyzed in the frame of large lattice-relaxed deep levels. We have determined the spectral dependence for the optical cross section and obtain an optical ionization energy of 0.83 eV.

On the negative Hubbard correlation energy of the DX center in In-doped CdMnTe

Persistent photoeffects have been investigated in indium doped Cd1−xMnxTe of manganese content x=0.1, by means of photocapacitance and photoconductivity transient measurements run at 77 K. The transients are superpositions of two exponents with short and long time constants. The two exponents have been attributed to the two-stage ionization of two energy states of the DX centers present in the material. A detailed analysis of photoionization kinetics leads to the conclusion that the DX center which is responsible for the observed persistent photoeffects possesses negative effective Hubbard correlation energy. Thus the “fast” component of the phototransients corresponds to the ionization of the two-electron ground state of the DX center to an intermediate one-electron state. The “slow” component is a result of the photoionization of the electron from this state into the conduction band. The value of the optical ionization energy for the first transition is equal to E20=0.85 eV. Photoionization of an electr...

Zn3P2: new material for optoelectronic devices

Fundamental optical and electronic parameters of Zn3P2 are presented. Mg-Zn3P2 structures are examined as a solar energy converter and broad-range photodetector. A distinct photodichroism, observed for junctions prepared on oriented single crystal, is applied in light polarization step indicator.

Non-linear electrical effects in epitaxial graded-gap CdxHg1−xTe layers

Abstract A gradient of electron (hole) effective masses creates in semiconductors an internal electric field of frequency twice that of the applied field. The internal field is parallel to this gradient and is perpendicular to the variable applied field. This “warm carrier” effect has been measured in epitaxial Cd x Hg 1− x Te layers of various molar compositions. Measurements were performed at 77 and 300 K, with the frequency of applied field in the range 20 Hz to 12.5 kHz. A comparison between the simple model and the observed experimental data is discussed.

Capture barrier for DX centers in gallium doped Cd1−xMnxTe

We report on the capture barrier for the gallium related DX center in Cd0.99Mn0.01Te. In order to determine the barrier height, two methods were applied: an analysis of the persistent photoconductivity decay and the optical deep level transient spectroscopy technique. Over a range of temperatures varying from 77to105K, the capture barrier height, deduced from the decay time constants of photoconductivity, has been found to be equal to 0.22eV. An apparent hole trap, observed with the optical deep level transient spectroscopy, was attributed to the thermally activated capture cross section of a DX center with a 0.23eV capture barrier. The obtained data are close to 0.21eV, the value of the capture barrier which we determined earlier with the help of the deep level transient spectroscopy method.